How radiation therapy is done

The type of radiation used for Wilms tumors is called external beam radiation therapy. Radiation from a source outside the body is focused onto the cancer.

Before treatments start, the radiation team will take careful measurements with imaging tests such as CT or MRI scans to determine the correct angles for aiming the radiation beams and the proper dose of radiation. This planning session is called simulation. Your child may be fitted with a plastic mold that looks like a body cast to keep him or her in the same position during each treatment so that the radiation can be aimed more accurately.

Radiation is usually given 5 days a week for several weeks. Each treatment is much like getting an x-ray, although the dose of radiation is much stronger. For each session, your child lies on a special table while a machine delivers the radiation from precise angles. Each session lasts about 15 to 30 minutes, with most of the time being spent making sure the radiation is aimed correctly. The actual treatment time is much shorter. The treatment is not painful, but some younger children may be given medicine to make them drowsy or asleep before each treatment to help make sure they stay still.

Types of radiation therapy

Modern radiation therapy techniques help doctors aim the treatment at the tumor more accurately than in the past. These techniques may help increase success rates and reduce side effects.

Three-dimensional conformal radiation therapy (3D-CRT): 3D-CRT uses the results of imaging tests such as MRI and special computers to precisely map the location of the tumor. Radiation beams are then shaped and aimed at the tumor from different directions. Each beam alone is fairly weak, which makes it less likely to damage normal body tissues, but the beams converge at the tumor to give a higher dose of radiation there.

Intensity modulated radiation therapy (IMRT): IMRT is an advanced form of 3D therapy. Along with shaping the beams and aiming them at the tumor from several angles, the intensity (strength) of the beams can be adjusted to limit the dose reaching the nearby normal tissues. This lets doctors deliver a higher dose to the tumor. Many major hospitals and cancer centers now use IMRT.

Possible side effects of radiation therapy

Radiation is often an important part of treatment, but young children’s bodies are very sensitive to it, so doctors try to use as little as possible to help avoid or limit any problems. Radiation therapy can cause both short-term and long-term side effects, which depend on the dose of radiation and where it’s aimed.

Possible short-term effects include:

Effects on areas of skin that get radiation can range from mild sunburn-like changes and hair loss to more severe skin reactions.

Radiation to the abdomen (belly) can cause nausea or diarrhea.

Radiation therapy can make a child tired, especially after several days or weeks of treatment.

Possible long-term effects include:

Radiation to the kidney area can damage the kidneys. This is more likely to be a concern in children who need treatment in both kidneys.

Radiation can slow the growth of normal body tissues (such as bones) that get radiation, especially in younger children. In the past this led to problems such as short bones or a curving of the spine, but this is less likely with the lower doses of radiation used today.

Radiation to the chest area can affect the heart and lungs. This doesn't usually cause problems right away, but in some children it might lead to heart or lung problems as they get older.

In girls, radiation to the abdomen (belly) may damage the ovaries. This might lead to abnormal menstrual cycles or problems getting pregnant or having children later on.

Radiation slightly increases the risk of developing a second cancer in the area, usually many years after it is given. This doesn’t happen often with Wilms tumors because the amount of radiation used is low.